REQUIREMENTS of Gr. 91 TUBE & PIPE COMPONENTS 16 Jan. 2010 Prepared by Jaehong Oh This has been prepared as a Quality Control Tip based on Grade 91 Supplementary Technical Requirements of ALSTOM DESIGN STANDARD No. 2-2004 and Purchase Instruction to indoctrinate all Quality Personnel and/or whoever involved in Gr. 91 works on BARH-II Project in the APIL Durgapur shop. 1. Material Purchase Instruction: 1) SA213-T91: Purchase Instruction (P.I) No. P0B4 and STD No. 7-2008 2) SA182-F91 / SA335-P91 / SA336-F91 / SA369-FP91: P.I STD No. 6-2008 2. Forming: 1) After hot pressing (squeezing and sizing) and hot bending operations the entire component shall be Normalized and Tempered. 2) Hot adjustment to shape – If the 790 ℃ limit is exceeded during hot adjustment operation, then a full Normalizing and Tempering of the entire component must be performed. Therefore, implementation of hot adjustment procedure shall be strictly controlled and observed by Quality personnel 3) Cold Pressing (swaging, pointing, squeezing & sizing) – When a cold pressed component has a design temperature of 537 deg C or higher it shall be Normalized and Tempered of the entire component 4) Cold Bending: a) If R/D < 2.5, then the entire component shall be Normalized and Tempered. b) If 4 > R/D ≥ 2.5, then the bend region shall be heat treated at 730 – 770 ℃ for min. 30 minutes. c) If R/D ≥ 4, then no Post Forming Heat Treatment is required. 5) After hot forming of Fitting and Special Products, the entire component shall be Normalized and Tempered. 3. Welding: 1) Filler Metal Properties: In addition to the requirements of ASME/AWS, as a minimum Ni + Mn ≤ 1.2%, N ≥ (0.5 x Al + 0.03) % Therefore, MTR of filler metal shall be reviewed prior to beginning of welding. 2) Preheating: SMAW / FCAW / SAW: 205 ℃ minimum shall be maintained. GMAW / GTAW: 150 ℃ minimum shall be maintained. a) Tube butt welding – Joint by joint shall be preheated and welded. Do not welding two or more joints at the same time: Rosebud gas torch shall be used. Cutting torch is prohibited. b) Pipe/Header/Plate – Electric resistance heating pad shall be used. 3) Preheating Interruption: a) Once welding is started preheating temperature shall be maintained throughout the welding process without interruption until the welding is completed.

b) If a) is impractical to accomplish, the preheat may be interrupted, provided that at least 9.5mm thickness of weld is deposited or 25% of the weld groove is filled, whichever is greater. Then, temperature shall be dropped to below 95 ℃ and a hydrogen bake be performed immediately. 4) Interpass Temperature – Max. 400 ℃ 5) Following completion of welding, temperature shall be dropped to below 95 ℃, then PWHTed within eight (8) hours at temperature 730 – 775 ℃ for 1 hr / Inch of thickness, with a 30 minutes min. 6) If it is not possible to perform PWHT within 8 hours, Hydrogen Bake shall be performed at temp. 260 - 400 ℃ for 1 hr / Inch of thickness, up to max. 4 hours, with a 30 minutes min. (Prior to Hydrogen Bake, welds shall be dropped to below 95 ℃) Exemption of Hydrogen bake: tube and pipes OD ≤ 4.5” (115mm), and wall thickness up to 16mm. And then, the component is maintained at a temperature above 95 ℃ or kept in a dry environment until PWHT is initiated. The joint is not subjected to significant thermal reaction loads or other applied loads in the as-welded condition. 4. Normalizing and Tempering: 1) Normalizing temp. 1040 – 1080 ℃ for min. 10 minutes. 2) Prior to Tempering, temperature shall be dropped to below 95 ℃ 3) Tempering temp. 730 – 790 ℃ for 1 hr / Inch of thickness, with a 15 minutes min. If Gr. 91 weld is located in the tempering furnace, temp. range shall be 730 – 775 ℃ 4) For tubular products, or other thin walled products, decarburized layer (OD + ID) do not exceed 7% of specified MWT. Decarburization thickness shall be determined by performing microstructural analysis at 100X from each N+T+PWHT lot. 5. Surface Condition: PWHT is required when weld repair of surface imperfections such as grinding marks, arc strikes, etc. is conducted. Therefore, Weld Visual shall be inspected thoroughly prior to performing PWHT. 6. Hardness: Base material hardness range: 186 HB / 195HV (90.5HRB) to 245 HB / 257HV (23.6HRC / 100.6 HRB) After all shop fabrications, weld metal and HAZ shall be Min. 186 HB / 195HV (90.5HRB) and Max. 303 HB / 320HV (32.2HRC) 7. NDE Requirement: All required NDE shall be performed after PWHT. All nipple welds to headers shall be examined by fluorescent MT before and after PWHT as per the MQP 8. Weld Filler Metal Purchase Instruction: 1) P5W13 for SMAW 2) P5W14 for Auto GMAW 3) P5W15 for GTAW 4) P5W16 for SAW 5) P5W20 for FCAW